1. Field of the Invention
The present invention relates to wireless communication devices, and specifically to wireless communication devices that communicate with readers/writers in radio frequency identification (RFID) systems.
2. Description of the Related Art
Known article management systems include an RFID system in which a reader/writer communicates with RFID tags (also called wireless IC devices) in a noncontact manner, whereby information is transmitted between the reader/writer and the RFID tags. An RFID tag includes a wireless IC chip for processing wireless signals and an antenna for transmitting/receiving wireless signals, and predetermined information is transmitted/received as high-frequency signals between the antenna of an RFID tag and the antenna of a reader/writer via a magnetic field or an electric field.
Generally, dipole antennas are used as antennas of RFID tags, as described in Japanese Unexamined Patent Application Publication No. 2004-104344, Japanese Unexamined Patent Application Publication No. 2009-524363, and International Publication No. 2007/013168. A dipole antenna, which transmits/receives signals mainly using an electric field, has a long communication range when used by itself. However, when an object with a large relative dielectric constant or a large electroconductivity is in the vicinity of the antenna, the radiation characteristics are likely to change.